Fluorinated hydrophilic polymers

ABSTRACT

1) Hydrophilic fluoropolymers obtained by radical polymerization, in a precipitating medium, of a mixture of monomers composed of at least one monomer with a perfluoroalkyl side chain, of one or more ionic or ionizable hydrophilic monomer(s) and optionally of one or more nonionic hydrophilic monomer(s). 
     2) Use of these polymers as dispersants or thickeners and as additives in multipurpose fire-fighting emulsifiers.

FIELD OF THE INVENTION

The present invention relates to the field of hydrophilic polymers andhas more particularly as subject-matter hydrophilic fluoropolymersobtained by radical polymerization in a precipitating medium. Thesepolymers lower the surface tension of aqueous solutions; they are goodfoaming agents and they are more particularly advantageous asdispersants or thickeners and as additives in multipurpose fire-fightingemulsifiers.

BACKGROUND OF THE INVENTION

Hydrophilic polymers and more particularly those based on acrylamide, onmethacrylamide or on their N-substituted derivatives are well known andwidely used industrially. Acrylamide, methacrylamide and theirderivatives are very often copolymerized with other hydrophilic monomerscarrying anionic or cationic ionic or ionizable charges which confer, onthe hydrophilic polymer, specific properties suited to each application.These polymers are commonly used in the paper industry, in watertreatment or in metallurgy as flocculants for ores; they are also usedas thickening agents in numerous formulations, such as textile printingand cosmetic products.

The most widely used methods for preparing these polymers involveaqueous media; such is the case of polymerization in aqueous solution orof micellar polymerization but other methods, such as inverse emulsionpolymerization, are also practised. The polymerization is generallyinitiated by a radical-generating redox couple, such as, for example,the persulphate (S₂O₈ ²⁻)/metabisulphite (S₂O₅ ²⁻) couple, but also byazo or peroxide radical initiators. Other initiating systems can beused, such as UV rays, X rays, ultrasound or cobalt salts.

The copolymerization of acrylamide, of methacrylamide and of theirderivatives in a precipitating medium, in which the monomers are solubleand the polymer precipitates during its formation, is a method which ismore rarely used and which is disclosed in particular in Patents FR 1508 702, GB 1 328 742 and U.S. Pat. No. 3,336,269.

Acrylamide, methacrylamide and their derivatives can also becopolymerized with water-insoluble monomers possessing ahydrocarbonaceous hydrophilic side chain, such as, for example, fattyalcohol acrylates or methacrylates. The copolymers thus formed areassociative thickeners, the hydrophobic groups of which, in aqueoussolution, tend to form intermolecular associations, thus creating atransitory network. In aqueous solution, the viscosity of theseassociative polymers depends on the shear rate; the solution generallyexhibits a pseudoplastic nature, that is to say that its viscositydecreases with the increase in the shear rate. Such products aredisclosed in references [1] to [3], the list of which appears after theexamples of the present application.

Acrylamide, methacrylamide and their derivatives can also becopolymerized with monomers possessing a perfluoroalkyl hydrophobic sidechain, such as, for example, fluoroalcohol acrylates or methacrylates.The synthesis and the characterization of such hydrophilicfluoropolymers are described by Thieo E. Hogen-Esch and his coworkersand by other authors in references [4] to [12]. These fluorocopolymerswere prepared in aqueous medium in the presence of a cosolvent, such asacetone ([4]-[9]), and more rarely in aqueous medium in the absence ofcosolvent [12] or under bulk conditions [9], the polymerization reactionhaving been initiated by a redox couple which is a precursor of radicalsby oxidation/reduction ([4]-[9]), by a radical initiator which is aprecursor of radicals by thermal decomposition ([9]-[12]) or bytriphenylmethylcaesium in anionic polymerization in solution intetrahydrofuran. U.S. Pat. No. 4,891,306 discloses hydrophilicfluorocopolymers obtained by anionic or cationic polymerization; theseproducts are used in light-sensitive photographic materials.

In all the cases cited above, the hydrophilic fluorocopolymers aresynthesized under bulk conditions or in aqueous medium in the presenceof surfactants, the purpose of which is to dissolve the hydrophobicfluoromonomers inside the micelles. The surfactants preferably used arefluorosurfactants, the perfluoroalkyl side chain of which is compatiblewith fluoromonomers, which makes possible the dissolution of thesemonomers. The hydrophilic fluoropolymers obtained by polymerization inaqueous medium exhibit, as common characteristic, a high molecularweight, which leads to very viscous aqueous solutions, resulting in theuse of such products as viscosifying agents. In many cases, the presenceof fluorosurfactants interferes with the subsequent use of the polymers,which makes it necessary to resort to precipitation of the polymer froma large excess of solvent, followed by washing the polymer. Thisprecipitating and washing stage, which is additional to the synthesis,has to be carried out with large amounts of solvents, such as, forexample, alcohols, which increases the manufacturing cost and produceseffluents laden with surfactants. In the case of the polymerization in aprecipitating medium, used in the context of the present invention, itis much easier and faster to recover the polymer in the powder form.Although starting from monomers of the same nature as those describedabove, namely acrylamide or methacrylamide derivatives and monomerscomprising a perfluoroalkyl side chain, the hydrophilic fluoropolymersforming the subject-matter of the present invention are distinguishedfrom the above in several respects, the main ones of which are thepreparation process proper, the content of fluoromonomers incorporatedin the polymer and the nature of the radical-initiating agents. Thesedifferences are reflected by very different behaviours from the viewpoint of the applicative properties.

The hydrophilic fluoropolymers according to the invention can, forexample, be used as additives in multipurpose fire-fighting emulsifiers,that is to say emulsifiers intended for the extinguishing of hydrocarbonfires and polar liquid fires.

Fire-fighting emulsifiers comprising hydrophilic fluoropolymers havealready been disclosed, in particular in Patents FR 2 438 484, U.S. Pat.Nos. 4,563,287 and 4,606,832.

Acrylamide, methacrylamide and their N-substituted derivatives, used inthe context of the present invention, and the method for polymerizationin a precipitating medium are not mentioned in U.S. Pat. No. 4,563,287,which, for the extinguishing of cooking oil fires, discloses nonfoamingcompositions, whereas the emulsifiers comprising a hydrophilicfluoropolymer according to the present invention are foamingcompositions.

The extinguishing compositions disclosed in U.S. Pat. No. 4,606,832,also intended for combating cooking oil fires, involvedbromofluorohydrocarbons and/or bromochlorofluorohydrocarbons, which isnot the case in the present invention, and are not fire-fightingemulsifiers having foaming properties, as in the case of the presentinvention.

Patent FR 2 438 484, which does not mention acrylamide, methacrylamideor their N-substituted derivatives, indicates that the polymers can beobtained by solution polymerization. In point of fact, solutionpolymerization, applied to the hydrophilic fluoropolymers according tothe invention, does not result in successful products; it is necessaryto resort to polymerization in a precipitating medium.

SUMMARY OF INVENTION

A subject-matter of the present invention is therefore hydrophilicfluoropolymers obtained by radical polymerization, in a precipitatingmedium, of a mixture of monomers composed, by weight, of:

(a) 0 to 49% of at least one nonionic hydrophilic monomer, preferably 25to 45%, more preferably still 35 to 45%;

(b) 20 to 75% of at least one monomer comprising a perfluoroalkylradical, preferably 25 to 60%, more preferably still 25 to 50%; and

(c) 5 to 75% of one or more ionic or ionizable hydrophilic monomers,preferably 5 to 35%, more preferably still 5 to 20%.

These polymers have foaming properties; they lower the surface tensionof aqueous solutions and are particularly advantageous as additives inmultipurpose fire-fighting emulsifiers, that is to say emulsifiersintended for combating hydrocarbon fires and polar liquid fires. Theyare advantageous in particular in preventing the resurgence of the fire,in the case of combating polar liquid fires.

A fourth monomer can also be used. It can in particular be a monomerwhich acts as crosslinking agent, for example during the application ofthe polymer to the fire to be combated.

The method used to prepare these hydrophilic fluoropolymers ispolymerization in a precipitating medium; it exhibits the advantage ofgenerating polymers of low molecular weight and therefore products oflow viscosity, of making use of a single solvent, which can easily beregenerated and reused, and of not requiring the use of surfactantswhich might interfere with the application and which it would thereforebe necessary to extract from the medium. The solvent used for thispolymerization in a precipitating medium can be distilled off and thenreplaced with water or a water/cosolvent mixture. The final product isthen provided in the form of an aqueous dispersion of the polymer.Depending on the operating conditions, such as the relative contents ofthe various monomers, the concentration of radical initiator, the totalinitial concentration of monomers and the polymerization temperature, itis possible to obtain a complete range of polymers according to theinvention which differ in their molecular weight, their fluorine contentand their level of anionic and/or cationic charges.

Mention may be made, as nonlimiting examples of nonionic hydrophilicmonomers (a), of:

N-vinyl-2-pyrrolidone and its derivatives, such asN-vinyl-3-methyl-2-pyrrolidone, N-vinyl-4-methyl-2-pyrrolidone,N-vinyl-5-methyl-2-pyrrolidone or N-vinyl-3,3-dimethyl-2-pyrrolidone;

ethylene glycol acrylate or methacrylate;

polyethylene glycol or polyethylene glycol ether acrylates ormethacrylates corresponding to the general formula:

CH₂═CR¹—CO(OCH₂CH₂)_(k)—OR  (I)

in which R represents a hydrogen atom or a methyl or ethyl radical, k isan integer ranging from 1 to 50 and R¹ represents a hydrogen atom or amethyl radical;

acrylamide, methacrylamide and their N-substituted derivativescorresponding to the following general formula:

CH₂═CR¹—CONR²R³  (II)

in which R¹ has the same meaning as above and the R² and R³ symbols,which are identical or different, each represent a hydrogen atom or analkyl or hydroxyalkyl radical comprising from 1 to 3 carbon atoms.

Mention may be made, as nonlimiting examples of hydrophilic monomers offormula (II), of acrylamide, N-methylacrylamide, N-ethylacrylamide,N,N-dimethylacrylamide, N-methyl-N-ethylacrylamide,N-(hydroxymethyl)acrylamide, N-(3-hydroxypropyl)acrylamide,N-(2-hydroxyethyl)acrylamide, methacrylamide, N-methylmethacrylamide,N-ethylmethacrylamide, N,N-dimethylmethacrylamide,N-(hydroxymethyl)methacrylamide, N-(3-hydroxypropyl)methacrylamide andN-(2-hydroxyethyl)methacrylamide.

Acrylamide, methacrylamide and their N-substituted derivatives describedabove will preferably be chosen and more particularly acrylamide andmethacrylamide.

The fluoromonomers (b) are monomers comprising a linear or branchedperfluoroalkyl radical comprising from 2 to 20 carbon atoms. The choiceis preferably made of acrylates or methacrylates of fluoroalcoholscorresponding to the following general formula:

in which R_(f) represents a linear or branched perfluoroalkyl radicalcomprising from 2 to 20, preferably from 4 to 16, carbon atoms, R⁴represents a hydrogen atom or a methyl radical and B represents adivalent linkage bonded to O via a carbon atom which can comprise one ormore oxygen, sulphur and/or nitrogen atoms. Mention may be made, withoutimplied limitation, of acrylates or methacrylates of the fluoroalcoholscorresponding to the following formulae:

R_(f)—(CH₂)_(n)—(X)_(p)—(CH₂)_(m)—OH

R_(f)—(CH₂)_(r)—(OCH₂CH₂)_(q)—OH

R_(f)—CH₂═CH—(CH₂)_(m)—OH

in which R_(f) has the same meaning as in the formula (III), Xrepresents an oxygen or sulphur atom or a —COO—, —OCO—, —CONR⁵— or—SO₂NR⁵— group, R⁵ denoting a hydrogen atom or a methyl or ethylradical, n represents an integer ranging from 0 to 20 (preferably equalto 0 or 2), p is equal to 0 or 1 and the m, q and r symbols, which areidentical or different, each represent an integer ranging from 1 to 20(preferably equal to 2 or 4), n not being zero if X is an oxygen orsulphur atom or an —OCO— group.

Use is preferably made of acrylates or methacrylates of thefluoroalcohols corresponding to the following formulae:

R_(f)—CH₂CH₂—OH

or

R_(f)—CH₂CH₂—SO₂NR⁵—CH₂CH₂—OH

in which R_(f) and R⁵ have the same meanings as above.

Mention may be made, without implied limitation, as examples of ionichydrophilic monomers (c) or hydrophilic monomers (c) which can beionized by varying the pH which can be used in the context of theinvention, of:

acrylic acid, methacrylic acid and their alkali metal or quaternaryammonium ion salts;

monoolefinic sulphonic acid derivatives and their alkali metal salts,such as, for example, sodium ethylenesulphonate, sodiumstyrenesulphonate and 2-acrylamido-2-methylpropanesulphonic acid;

vinylpyridinium halides, such as, for example, 4-vinylpyridiniumchloride;

acrylates or methacrylates of the aminoalcohols corresponding to thefollowing formulae:

HO—Y—NR⁶R⁷ or HO—Y—N^(⊕)R⁶R⁷R⁸A⁻

in which the R⁶, R⁷ and R⁸ symbols, which are identical or different,each represent an alkyl or hydroxyalkyl radical comprising 1 to 4 carbonatoms, Y represents an alkylene or hydroxyalkylene radical comprisingfrom 1 to 4 carbon atoms and A⁻ is any monovalent anion;

acrylates or methacrylates of cyclic aminoalcohols, such as, forexample, 2-piperidinoethanol and 2-(pyrrolidin-1-yl)ethanol.

The hydrophilic fluoropolymers according to the invention are preparedby polymerization in a precipitating medium in the absence of surfactantor of any other stabilizing agent.

The polymerization in a precipitating medium makes it possible toachieve, depending on the choice of the solvent, much lower molecularweights than in the case of the polymerization in aqueous solution.Thus, it is not necessary to resort to transfer agents, such as alkylmercaptans, in order to regulate the length of the chains; thisadvantage can be turned to good account if products having low molecularweights, therefore products whose aqueous solutions have very littleviscosity, are desired. The achievement of low molecular weights for thehydrophilic fluoropolymers makes it possible to prepare aqueoussolutions of low viscosity; this point is important for the use of thepolymers in multipurpose fire-fighting emulsifiers where, for operatingreasons, low viscosities are preferably sought.

The polymerization reaction takes place in an organic solvent in whichthe monomers and the radical initiator are completely soluble and inwhich the polymer obtained is insoluble, so that it precipitates duringits formation. The polymerization solvent preferably has a shorthydrocarbonaceous chain, such as acetonitrile and lower alcohols. Thechoice of the polymerization solvent depends on the nature of themonomers (a), (b) and (c); it is essential, at the beginning of thereaction, for all the reactants to be completely soluble in the solventat a temperature corresponding to that of the beginning of thepolymerization. The total concentration of monomers in the solvent isadvantageously between 100 and 500 g/liter, preferably between 150 and350 g/liter. The solvent is preferably chosen from lower alcoholscomprising from 1 to 4 carbon atoms, such as, for example, methanol,ethanol, isopropanol or tert-butanol. The reaction can be carried outbatchwise or continuously, it being possible for the monomers (a), (b)and (c) to be introduced independently into the reactor at differenttimes.

The radical initiator can be an initiator of azo type, such as, forexample, azobisisobutyronitrile or 4,4′-azobis(cyanopentanoic acid), andtheir derivatives possessing a hydrocarbonaceous or perfluoroalkyl sidechain. The preparation of azo initiators possessing a perfluoroalkylchain is described in reference [13].

The initiator can also be of peroxide type, such as, for example,dicyclohexyl peroxydicarbonate, benzoyl peroxide or di-tert-butylperoxide. It can also be a perester possessing a hydrocarbonaceous orperfluoroalkyl side chain. The preparation and the use of perfluoroalkylperester initiators is described in references [14] and [15].

The concentration of the initiator can vary from 0.1 to 10 mol % withrespect to the total number of moles of monomers but more particularlybetween 0.6 and 2%. Depending on the type of radical initiator used andon the boiling point of the solvent, the polymerization temperature isbetween 50 and 100° C., preferably between 70 and 90° C. The reactioncan be carried out, for example, at reflux of the solvent; in this case,the condenser condenses and returns the solvent in the liquid form tothe reaction medium. The addition of the radical initiator can becarried out in a single step at the beginning of the reaction but it ispreferable to add it in several fractions or else continuously as thismakes possible better incorporation of the fluoromonomer in the polymer.It is preferable to employ the radical initiator already in solution andto use, in this case, the reaction solvent.

At the end of the reaction, the hydrophilic fluoropolymer according tothe invention can be recovered in the solid form by filtration. Thereaction solvent can also be removed from the reaction medium byevaporation and replaced with water, so as to obtain the polymeraccording to the invention in the form of an aqueous solution.

The hydrophilic fluoropolymers according to the invention lower thesurface tension of aqueous solutions; they have a good foaming power andcan, for example, be used as additives in multipurpose fire-fightingemulsifiers, that is to say fire-fighting emulsifiers intended forcombating hydrocarbon fires, such as fires in which the hydrocarbons arepetrols, oils, diesel oil, fuel oil, heptane, hexane or cyclohexane, orpolar liquid fires, such as fires in which the polar liquids arealcohols (for example, methanol, ethanol and isopropanol), ketones (forexample, dimethyl ketone and methyl isobutyl ketone), esters (forexample, n-butyl acetate) and ethers (for example, methyl tert-butylether).

Fire-fighting emulsifiers are liquid compositions intended for combatingcombustible liquid fires (in which the combustible liquids arehydrocarbons and/or polar liquids). At the time of use, the emulsifiersare diluted in municipal water or seawater, generally at a concentrationby volume of 3% (that is to say, 3 volumes of emulsifier per 97 volumesof water) or 6% (6 volumes of emulsifier per 94 volumes of water) butalso, and more rarely 1% (1 volume of emulsifier per 99 volumes ofwater). After diluting the emulsifiers, as the amount of activematerials necessary to satisfy the minimum extinguishing performancerequired is identical in all cases of dilution, emulsifiers which aredilutable to 3% are therefore twice as concentrated as those which aredilutable to 6%; they make it possible for the users to store smalleramounts of emulsifier, to save space and to reduce their storage costs.The foaming solution is obtained by diluting the emulsifier with water.This foaming solution passes through a fire hose nozzle where mechanicalagitation takes place with incorporation of air, which generates anextinguishing foam used to combat combustible liquid fires.

When the polymers according to the invention are incorporated in theemulsifiers, they improve the stability of the extinguishing foams on apolar liquid and thus their extinguishing performance on fires of thistype. Their content in the emulsifiers can generally range from 0.1 to10% by weight and preferably from 0.2 to 5% by weight.

The emulsifiers in which the hydrophilic fluoropolymers can beincorporated are of two types, depending upon the origin of theirfoaming base. Synthetic emulsifiers, the foaming base of which iscomposed of at least one hydrocarbonaceous surface-active agent, andprotein emulsifiers, the foaming base of which is composed of an animalprotein hydrolysate, are distinguished. These two types of emulsifierscan comprise, according to their destination, one or morefluorosurfactants, one or more foam-stabilizing cosolvents, ahydrophilic polymer of high molecular weight of the polysaccharide typewith a thixotropic and alcohol-repellent nature, an antifreezing agent,a corrosion-inhibiting agent, a preservative, a pH stabilizer orinorganic salts in which the cation is divalent, such as, for example,the magnesium ion or the calcium ion.

Multipurpose fire-fighting emulsifiers comprising a hydrophilic polymeraccording to the invention are used for combating hydrocarbon fires andpolar liquid fires. Their performances can be evaluated by means of thefollowing tests:

Extinguishing Efficiency on a Polar Liquid

150 ml of acetone are poured into a circular metal container with aninternal diameter of 12 cm. Moreover, an aqueous solution composed ofthe emulsifier diluted to 3 or 6% in municipal water is prepared. Thereis available a rotary stirrer composed of a motor and a metal rod, atthe end of which are attached paddles which produce a mechanical effectwhen the rod is being rotated; the rotational speed is adjustable from 0to 2800 rev/min. The rod is introduced into the bottom of a cylindricalcontainer equipped with an inlet orifice situated at the bottom and withan outlet orifice situated at the top. A metering pump transfers, viathe inlet orifice, the aqueous solution to the bottom of the cylindricalcontainer; foam is produced on contact with the rotating paddles, whichfoam is discharged as it is formed, via the outlet orifice. Thethroughput of the pump and the rotational speed of the rod are adjustedso that foam is continuously produced with a stationary foam throughputequal to 36±2 g/min (unless otherwise indicated).

When the foam throughput is stabilized, the acetone is ignited. Afterthe acetone has burnt for 90 seconds, the foam is poured into the metalcontainer via a single point situated on the circumference. When theacetone has been completely extinguished, the extinguishing time isrecorded. The amount of foam poured in order to extinguish the fire seatis calculated by multiplying the time by the throughput. The emulsifierswith the best performance on a polar liquid are those for which theamount of foam poured is as low as possible.

Resistance of the Foam to Reignition

This parameter can be evaluated if the extinguishing time is less than120 s. In this case, the foam is poured over the acetone even after thefire seat has been extinguished. The operation in which foam is run inlasts a total of 120 s. 60 s after the pouring of the foam has beenhalted, the contents of a reignition vessel (metal container with adiameter of 55 mm and a height of 40 mm filled with acetone to a heightof 20 mm) are ignited. The reignition vessel is placed at the centre ofthe metal container described above, the surface of the fuel present inthe said container being kept covered with foam. The time at the end ofwhich the flames destroy the foam and spread in a lasting fashion overthe surface of the metal container is recorded. The greater this time,the better the ability of the foam to prevent the resurgence of thefire.

EXAMPLES

In the following examples, which illustrate he invention withoutlimiting it, the percentages shown are expressed by weight and someconstituents used are denoted for simplicity by the followingabbreviations:

A1=2-(perfluorooctyl)ethyl acrylate of formula:

CH₂═CH—COO—C₂H₄—(CF₂)₇CF₃

A2=mixture of 2-(perfluoroalkyl)ethyl acrylates of formula:

CH₂═CH—COO—C₂H₄—(CF₂)_(n)CF₃

having the following composition by weight:

N % 5 1 7 63  9 25  11  9 13  3

A3=mixture of 2-(perfluoroalkyl)ethyl methacrylates of formula:

CH₂═C(CH₃)—COO—C₂H₄—(CF₂)_(n)CF₃

having the same composition by weight as A2

B1=acrylic acid of formula:

CH₂═CH—COOH

B2=N-[2-(acryloyloxy)ethyl]-N,N,N-trimethylammonium chloride of formula:

CH₂═CH—COO-C₂H₄—N^(⊕)(CH₃)₃Cl⁻

B3═2-acrylamido-2-methylpropanesulphonic acid of formula:

CH₂═CH—C(O)—NH—C(CH₃)₂—CH₂SO₃H

C1=27% aqueous/alcoholic solution of the fluorobetaine of formula:

Examples 1 and 2

a) Synthesis

225 ml of isopropanol are incorporated in a 1 liter reactor equippedwith a thermometer, a reflux condenser, a nitrogen inlet and amechanical stirrer. Stirring is begun and then the reaction medium isbrought to a temperature of 80° C. under a nitrogen flow. Furthermore,the solutions S1 and S2, which appear in the following table, areprepared.

Example 1 Example 2 Solution Acrylamide 27 g (0.38 mol) 27 g (0.38 mol)S1 B1 7.4 g (0.10 mol) 7.4 g (0.10 mol) A3 20 g (0.03 mol) 30 g (0.05mol) Isopropanol 195 g (250 ml) 195 g (250 ml) Solution Azobisiso- 2.5 g(0.015 mol) 2.5 g (0.015 mol) S2 butyronitrile N-methyl- 25 g 25 gpyrrolidone Isopropanol 19.5 g (25 ml) 19.5 g (25 ml)

S1 and S2 are introduced simultaneously into the reactor over a time of3 h, followed for 30 minutes by the introduction of the solution S2alone.

After washing the polymer thus obtained with isopropanol and withacetone, the latter is dried for 14 h at 40° C. and then dissolved in a70/30% by weight water/1,2-propanediol mixture. The dispersion obtainedcomprises 30% of water-soluble polymer. The pH of this dispersion isadjusted to 7.5 using diethanolamine.

b) Evaluation as Synthetic Fire-fighting Emulsifier

A series of synthetic fire-fighting emulsifiers is prepared byproceeding, for each of them, in the following way:

A mass of water-soluble polymer solution corresponding to 0.76 g of thehydrophilic fluoropolymer prepared above, 15 g of butyl diglycol and 5 gof solution C1 are added to 50 g of a 1% aqueous polysaccharide solutionprepared by addition to water at room temperature with vigorous stirringof the polysaccharide Actigum CX9YL1 from System Bio-Industries in thepowder form. The emulsifier is then made up to 100 g by addition ofwater. A fire-fighting emulsifier is obtained which is diluted to 3%with municipal water. The resulting solution, subjected to the testsdescribed above, exhibits the characteristics given in the followingtable:

Extinguishing efficiency on acetone Polymer of Extinguishing Mass offoam Reignition Example time^((a)) poured time 1 89 s 59 g 153 s 2 82 s55 g 187 s ^((a))For the test of extinguishing efficiency on acetone,throughput of the foam set at 40 g/min.

Example 3

a) Synthesis

Example 1 is repeated while replacing B1 with 21.27 g of B3.

b) Evaluation as Synthetic Fire-fighting Emulsifier

The evaluation is carried out as in Example 1. The results of the testsare as follows:

Extinguishing time: 92 s (foam throughput 40 g/min)

Mass of foam poured: 61 g

Reignition time: 168 s

Examples 4 and 5

a) Synthesis

The synthesis is carried out as in Example 1 but the compositions of thesolutions are given in the following table:

Example 4 Example 5 Solution Acrylamide 27 g (0.38 mol) 29.2 g (0.41mol) S1 B1 5.2 g (0.07 mol) 5.2 g (0.07 mol) B2 6 g (0.03 mol) 0   A3 30g (0.05 mol) 30 g (0.05 mol) Isopropanol 195 g (250 ml) 195 g (250 ml)Solution Azobisiso- 2.5 g (0.015 mol) 2.5 g (0.015 mol) S2 butyronitrileN-methyl- 25 g 25 g pyrrolidone Isopropanol 16.5 g (25 ml) 16.5 g (25ml)

b) Evaluation as Synthetic Fire-fighting Emulsifier

Two synthetic fire-fighting emulsifiers are prepared by proceeding asfor Example 1. The results of the tests are collated in the followingtable:

Extinguishing efficiency on acetone Polymer of Extinguishing Mass offoam Reignition Example time^((a)) poured time 4 57 s 38 g 198 s 5 76 s52 g 190 s ^((a))For the test of extinguishing efficiency on acetone,throughput of the foam set at 40 g/min.

Examples 6 and 7

a) Synthesis

The synthesis is carried out as in Example 1 but the compositions of thesolutions are given in the following table:

Example 6 Example 7 Solution Acrylamide 27 g (0.38 mol) 29.2 g (0.41mol) S1 B1 5.2 g (0.07 mol) 5.2 g (0.07 mol) B2 6 g (0.03 mol) 6 g (0.03mol) A2 29.3 g (0.05 mol) 29.3 g (0.05 mol) Solvent: Isopropanolt-butanol 195 g (250 ml) 196 g (250 ml) Solution Azobisiso- 2.5 g (0.015mol) 2.5 g (0.015 mol) S2 butyronitrile N-methyl- 25 g 25 g pyrrolidoneSolvent: Isopropanol t-butanol 19.5 g (25 ml) 19.5 g (25 ml)

In the case of Example 7, t-butanol is used instead of the 225 ml ofisopropanol mentioned in Example 1.

b) Evaluation as Synthetic Fire-fighting Emulsifier

By proceeding as in Example 1, the following results are obtained:

Extinguishing efficiency on acetone Polymer of Extinguishing Mass offoam Reignition Example time^((a)) poured time 6  72 s  48 g 182 s 7 150s 100 g — ^((a))For the test of extinguishing efficiency on acetone,throughput of the foam set at 40 g/min.

Example 8

a) Synthesis

600 ml of isopropanol are incorporated in a 5 liter reactor equippedwith thermometer, a nitrogen inlet, a mechanical stirrer and a Dean andStark trap filled with isopropanol surmounted by a reflux condenser.Stirring is begun and then the reaction medium is brought to atemperature of 80° C. under a nitrogen flow.

Furthermore, the following solutions are prepared:

Solution S1:

158.32 g (2.22 mol) of acrylamide

30.36 g (0.42 mol) of B1

35 g (0.18 mol) of B2

175.20 g (0.30 mol) of A3

847.8 g (1080 ml) of isopropanol

Solution S2:

29.4 g of azobisisobutyronitrile

400 ml of a 50/50 isopropanol/N-methylpyrrolidone mixture.

The solution S1 and 200 ml of the solution S2 are run in over 3 h. Thereaction medium is subsequently kept stirred under nitrogen at thereflux temperature of the isopropanol for 2 h.

620 ml of isopropanol are distilled off. 600 ml of distilled water areheated to 70° C. The first 400 ml are added in 80 ml portions. A totalof 730 ml of azeotrope is removed from the reactor. 250 g of1,2-propanediol are added to the reaction medium. The solids content ofthe dispersion is adjusted to 31.5% by addition of water and the pH to6.7 by addition of diethanolamine.

b) Evaluation as Synthetic Fire-fighting Emulsifier

By proceeding as in Example 1, the following results are obtained:

Extinguishing time: 63 s (foam throughput 40 g/min)

Mass of foam poured: 42 g

Reignition time: 180 s

Although the invention has been described in conjunction with specificembodiments, it is evident that many alternatives and variations will beapparent to those skilled in the art in light of the foregoingdescription. Accordingly, the invention is intended to embrace all ofthe alternatives and variations that fall within the spirit and scope ofthe appended claims. The foregoing references are hereby incorporated byreference.

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[10] M. Yassini and T. E. Hogen-Esch—Polymer Preprints (1994), 35 (1),p. 478.

[11] Y. X. Zhang, A. H. Da and T. E. Hogen-Esch—Polymer Preprints(1989), 30 (2), p. 338.

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What is claimed is:
 1. Hydrophilic fluoropolymers obtained by radicalpolymerization, in a precipitating medium, of a mixture of monomerscomprised, by weight, of: (a) 25 to 49% of at least one nonionichydrophilic monomer selected from the group consisting ofN-vinyl-2-pyrrolidone, derivative of N-vinyl-2-pyrrolidone, acrylamide,methacrylamide, and an N-substituted compound having the formula ofCH₂═CR¹—CONR²R³ wherein R¹ represents a hydrogen atom or a methylradical; and R² and R³ are each independently a hydrogen atom or analkyl or hydroxyalkyl radical comprising from 1 to 3 carbon atoms; (b)20 to 75% of at least one monomer comprising a perfluoroalkyl radical;and (c) 5 to 75% of one or more ionic or ionizable hydrophilic monomers.2. Hydrophilic fluoropolymer according to claim 1, wherein thefluoromonomer or fluoromononers (b) are acrylic or methacrylic monomerscorresponding to the following formula:

in which R_(f) represents a linear or branched perfluoroalkyl radicalcomprising from 2 to 20 carbon atoms, B represents a divalent linkagebonded to O via a carbon atom which optionally comprises at least oneoxygen, sulphur and/or nitrogen atom and R⁴ represents a hydrogen atomor a methyl radical.
 3. Hydrophilic fluoropolymer according to claim 2,wherein B is a divalent radical CH₂CH₂ or CH₂CH₂NR⁵SO₂CH₂CH₂ in which R⁵represents a hydrogen atom or a methyl or ethyl radical.
 4. Hydrophilicfluoropolymer according to claim 1, wherein the ionic or ionizablehydrophilic monomer or monomers are selected from: acrylic acid,methacrylic acid and their aklali metal or quaternary ammonium ionssalts; monoolefinic sulphonic acid compounds and their alkali metalsalts, including sodium ethylenesulphonate, sodium styrenesulphonate and2-acrylamido-2-methylpropanesulphonic acid; acrylates or methacrylatesof the aminoalcohols corresponding to the following formulae: HO—Y—NR⁶R⁷or HO—Y—N^(⊕)R⁶R⁷R⁸A⁻ in which the R⁶, R⁷ and R⁸ symbols, which areidentical or different, each represent an alkyl or hydroxyalkyl radicalcomprising 1 to 4 carbon atoms, Y represents an alkylene orhydroxyalkylene radical comprising from 1 to 4 carbon atoms and A⁻ isany monovalent anion.
 5. Hydrophilic fluoropolymer according to claim 1,prepared by radical polymerization in a precipitating medium inacetonitrile or in an alcohol comprising from 1 to 4 carbon atoms. 6.Hydrophilic fluoropolymer according to claim 5, prepared by radicalpolymerization in a precipitating medium in ethanol, t-butanol orisopropanol.
 7. Hydrophilic fluoropolymer according to claim 1, indispersion in water or in a water/cosolvent mixture.
 8. Method forextinguishing fires comprising applying the hydrophilic fluoropolymeraccording to claim
 1. 9. Multipurpose fire-fighting emulsifiercomprising, by weight, from 0.1 to 10% of a hydrophilic fluoropolymeraccording to claim
 1. 10. Hydrophilic fuoropolymer according to claim 1,wherein the amount of nonionic hydrophilic monomer (a) is 25 to 45%, ofthe at least one monomer (b) is 25 to 60%, and of hydrophilic monomers(c) is 5 to 35%.
 11. Hydrophilic fluoropolymer according to claim 1,wherein the amount of nonionic hydrophilic monomer (a) is 35 to 45%, ofthe at least one monomer (b) is 25 to 50%, and of hydrophilic monomers(c) is 5 to 20%.
 12. Hydrophilic fluoropolymer according to claim 2,wherein R_(f) has from 4 to 6 carbon atoms.
 13. Multi purposefire-fighting emulsifier according to claim 9, wherein the